This study reports the green synthesis of ZnO nanoparticles using betel leaf (Piper betle) extract as a natural reducing and stabilizing agent. The synthesized ZnO nanoparticles were characterized by XRD, SEM, TEM, and UV-Vis spectroscopy, confirming their crystalline structure, spherical morphology, and an optical bandgap of 3.26 eV. The ZnO nanoparticles were then employed as the photoanode in dye-sensitized solar cells (DSSCs) using a natural dye extracted from mangosteen peel. Photovoltaic performance analysis revealed that DSSCs with a platinum (Pt) counter electrode exhibited a significantly higher efficiency (0.064%) compared to those using a carbon-based electrode (0.007%), demonstrating the superior catalytic activity of Pt in enhancing charge transport. These findings highlight the potential of ZnO nanoparticles synthesized via green methods for sustainable energy applications.